Leviticus — Chapter 18

The laws of sexual morality in Leviticus 18 open with God's declaration: \"I am the Lord your God.\" Lapide insists this is the ultimate foundation of sexual ethics: the prohibitions rest not merely on natural reason or social order, but on the holiness of God who gave them. He documents from Theodoret (quaest. 24) and Jerome (lib. 2 contra Jovinianum) the extreme corruption of the nations — Persians, Egyptians, Indians, Ethiopians — who practised incest with mothers, daughters, and sisters without legal shame.

Which if a man do, he shall live in them (Lev. 18:5). Lapide notes this refers primarily to temporal prosperity (Deut. 7:13; Aggai 2:20), not eternal life, as the Chaldean paraphrase indicates. Yet the Apostle (Rom. 10:4-5) uses this text to distinguish the Old and New Testaments: the Old promised life in temporal prosperity through observance; the New promises absolute eternal life. The saints of the Old Testament, keeping the law out of charity, also merited eternal life — but this was not the literal promise of the text.

No man shall approach to any who is near of kin to him, to uncover their nakedness (Lev. 18:6). The Hebrew \"nakedness\" (ervah) is a verecund metonymy for carnal knowledge. Lapide: the prohibited degrees of consanguinity and affinity are based on the natural law, not merely on Mosaic positive law. He cites Augustine (lib. 17 de Civitate): \"The more ancient the mingling of brothers and sisters, the more detestable it became when prohibited by religion.\" The natural law itself, Lapide argues, progressively reveals through reflection that kinship creates an impediment to licit union.

Thou shalt not give any of thy seed to be consecrated to the idol Moloch, nor defile the name of thy God (Lev. 18:21). Lapide: the offering of children to Moloch by passing them through fire was a practice of the Ammonites. The prohibition is placed among the sexual sins because it involves the disordering of the generative power — the same disordering that leads to the other sins forbidden in this chapter. Lapide notes that the defiling of God's name (v. 21) is the ultimate consequence of every sexual sin: it dishonours God who made us in His image.

Thou shalt not lie with mankind as with womankind: because it is an abomination (Lev. 18:22). Lapide declares sodomy a sin against nature, intrinsically disordered, and so condemned not merely by Jewish law but by the natural law visible to all peoples. He cites Aristotle (Eth. 7), Philo, and the Stoics as witnesses to nature's condemnation. The Canaanites were expelled from their land precisely for these crimes (Lev. 18:24-25), which shows that the land itself vomits out such offenders, as from a violation of the natural order.

Bestiality is declared a scelus — a crime — in v. 23. Lapide insists it is the most degraded of sexual sins because it violates the specific dignity of humanity by communion with the irrational. All three sins forbidden in Lev. 18:20-23 — adultery, sodomy, bestiality — are sins not merely against the Mosaic law but against the natural law written in human reason. This is why the Canaanites were punished before the Law was given to Moses: they sinned against what all men could know by nature.

Defile not yourselves with any of these things with which all the nations have been defiled (Lev. 18:24). Lapide insists that the sexual prohibitions of chapter 18 are not merely Mosaic positive law but expressions of the universal natural law, binding all nations. The Canaanites were condemned precisely because they violated these precepts before the Mosaic code was given, which proves they sinned against what all men can know by natural reason. This is the theological basis for the Church's universal moral teaching on sexual ethics.